One of the methods of electrically interconnecting a printed circuit board to other electronic system components, is to insert one or more longitudinal conductive stakes into the printed circuit board (PCB) substantially normal to the board surface. The stakes are connected electrically to circuit elements on the PCB. Wire harness or ribbon cables, for example, equipped with female end connectors are slipped over the stakes to make connection between the PCB and the other system components.
During PCB assembly, the conductive connector stakes, which typically have a rectangular cross section, are inserted into round holes in the PCB. On one side of the PCB, designated herein as the underside, the holes are each circumscribed by a metallic conductor. The diameter of the holes is designed to be smaller than the diagonal distance between the corners of the stakes to provide mechanical interference between the stakes and the PCB. The mechanical interference temporarily secures the stakes to the PCB prior to soldering.
Soldering is performed by a wave soldering machine. In this machine the underside of the PCB is first exposed to flux which conditions the PCB metallic conductors and the stakes for soldering. The underside of the PCB is then applied to a solder bath and the stakes are soldered to the metallic conductors circumscribing the respective holes, permanently securing the stakes to the PCB and making electrical contact with the elements on the PCB.
It has been determined that flux, applied to the underside of the PCB, will seep or wick up in the spaces between the round holes and rectangular stakes. In fact, the flux may cover the entire stakes. Since the flux is generally non conductive, it may prevent connectors subsequently inserted over the stakes from establishing electrical contact with the stakes.
It is not desirable to provide the PCB with rectangular holes to prevent the flux from wicking up to the upper parts of the stakes. If there is too much interference between the rectangular stakes and the rectangular holes, the PCB develops cracks. On the other hand, if there is too little interference between them, the stakes tend to slip out of the holes in the PCB during handling operations prior to soldering.
It is of course possible to cover the gap between the flat sides of the rectangular stakes and the round edges of the holes with a plastic header strip disposed on the top or component side of the PCB to prevent the flux from migrating to the upper end of the stakes. Another solution to this problem is to provide the stakes with collars to block the flux from contaminating the upper portions of the stakes. Both of these solutions are not cost effective, because they entail additional labor and material costs.